This invention generally relates to the shearing of discrete gobs from a vertically flowing stream of molten glass. More particularly, this invention relates to an improved mechanism and method to achieve this shearing. Specifically, this invention relates to such an improved mechanism which will cause a severed gob to turn from a vertical towards a horizontal orientation as it falls toward a forming mold.
The rectangular face plates of television picture tubes are produced in horizontally disposed, open top molds. It is desired in this operation to deliver severed charges or gobs of molten glass into the molds such that the vertical axis of the gob as severed lies along the horizontal axis of the mold. That is, the gob turns through about 90.degree. during its fall into the mold. In prior art methods of severing and tilting the gob, a pair of moving blades sever the glass and a knocker, attached to the underside of the lower blade, strikes the gob on its top end during severing and tilts the gob from a vertical towards a horizontal position. Differential blade thickness have also been used to achieve the same results. Also, a gob may be tilted by merely allowing the lower blade to become dull. The following U.S. Pat. Nos. are examples of the prior art: 1,950,339; 2,271,004; 2,812,619; and 3,607,208.
All of these prior art methods produce a blemish, known as a shear mark, on the finished glass product. This results from uneven cooling of the gob primarily due to excess contact between the hot gob surface and a relatively chilled surface portion of the shearing and tilting means. In the case of the dull shear blade, a ragged edge having thin glass spurs projecting from it was formed. I have found that the desired tilting may be achieved with minimal damage to the gob by causing the lower shear blade to over-travel the center of the glass stream during the cutting stroke.